Structures and methods for deploying electrode elements

ABSTRACT

An electrode support structure comprises a guide body having at its distal end a flexible spline leg. The spline leg is flexed to define an arcuate shape to facilitate intimate contact against tissue. An electrode element is carried by the spline leg for movement along its axis. The structure includes a control element coupled to the electrode element. The control element remotely imparts force to move the electrode element along the axis of the spline leg. Therefore, in use, the physician can cause the electrode element to travel along a path that the spline leg defines, without otherwise changing the location of the guide body.

FIELD OF THE INVENTION

[0001] The invention relates to systems and methods for ablatingmyocardial tissue for the treatment of cardiac conditions.

BACKGROUND OF THE INVENTION

[0002] Normal sinus rhythm of the heart begins with the sinoatrial node(or “SA node”) generating an electrical impulse. The impulse usuallypropagates uniformly across the right and left atria and the atrialseptum to the atrioventricular node (or “AV node”). This propagationcauses the atria to contract.

[0003] The AV node regulates the propagation delay to theatrioventricular bundle (or “HIS” bundle). This coordination of theelectrical activity of the heart causes atrial systole duringventricular diastole. This, in turn, improves the mechanical function ofthe heart.

[0004] Today, as many as 3 million Americans experience atrialfibrillation and atrial flutter. These people experience an unpleasant,irregular heart beat, called arrhythmia. Because of a loss ofatrioventricular synchrony, these people also suffer the consequences ofimpaired hemodynamics and loss of cardiac efficiency. They are more atrisk of stroke and other thromboembolic complications because of loss ofeffective contraction and atrial stasis.

[0005] Treatment is available for atrial fibrillation and atrialflutter. Still, the treatment is far from perfect.

[0006] For example, certain antiarrhythmic drugs, like quinidine andprocainamide, can reduce both the incidence and the duration of atrialfibrillation episodes. Yet, these drugs often fail to maintain sinusrhythm in the patient.

[0007] Cardioactive drugs, like digitalis, Beta blockers, and calciumchannel blockers, can also be given to control the ventricular response.However, many people are intolerant to such drugs.

[0008] Anticoagulant therapy also combats thromboembolic complications.

[0009] Still, these pharmacologic remedies often do not remedy thesubjective symptoms associated with an irregular heartbeat. They also donot restore cardiac hemodynamics to normal and remove the risk ofthromboembolism.

[0010] Many believe that the only way to really treat all threedetrimental results of atrial fibrillation and flutter is to activelyinterrupt all the potential pathways for atrial reentry circuits.

[0011] James L. Cox, M.D. and his colleagues at Washington University(St. Louis, Mo.) have pioneered an open heart surgical procedure fortreating atrial fibrillation, called the “maze procedure.” The proceduremakes a prescribed pattern of incisions to anatomically create aconvoluted path, or maze, for electrical propagation within the left andright atria, therefore its name. The incisions direct the electricalimpulse from the SA node along a specified route through all regions ofboth atria, causing uniform contraction required for normal atrialtransport function. The incisions finally direct the impulse to the AVnode to activate the ventricles, restoring normal atrioventricularsynchrony. The incisions are also carefully placed to interrupt theconduction routes of the most common reentry circuits.

[0012] The maze procedure has been found very effective in curing atrialfibrillation. Yet, despite its considerable clinical success, the mazeprocedure is technically difficult to do. It requires open heart surgeryand is very expensive. Because of these factors, only a few mazeprocedures are done each year.

[0013] It is believed the treatment of atrial fibrillation and flutterrequires the formation of long, thin lesions of different lengths andcurvilinear shapes in heart tissue. Such long, thin lesion patternsrequire the deployment within the heart of flexible ablating elementshaving multiple ablating regions. The formation of these lesions byablation can provide the same therapeutic benefits that the complexincision patterns that the surgical maze procedure presently provides,but without invasive, open heart surgery.

[0014] With larger and/or longer multiple electrode elements comes thedemand for more precise control of the ablating process. The delivery ofablating energy must be governed to avoid incidences of tissue damageand coagulum formation. The delivery of ablating energy must also becarefully controlled to assure the formation of uniform and continuouslesions, without hot spots and gaps forming in the ablated tissue.

[0015] The task is made more difficult because heart chambers vary insize from individual to individual. They also vary according to thecondition of the patient. One common effect of heart disease is theenlargement of the heart chambers. For example, in a heart experiencingatrial fibrillation, the size of the atrium can be up to three timesthat of a normal atrium.

[0016] One objective of the invention is to provide tissue ablationsystems and methods providing beneficial therapeutic results withoutrequiring invasive surgical procedures.

[0017] Another objective of the invention is to provide systems andmethods that simplify the creation of complex lesions patterns in bodytissue, such as in the heart.

SUMMARY OF THE INVENTION

[0018] A principal-objective of the invention is to provide improvedstructures and methodologies for deploying electrode elements in contactwith tissue. In a preferred implementation, the structures andmethodologies that embody features of the invention make possible thecreation of long, thin lesion patterns in tissue for the treatment of,for example, heart conditions like atrial fibrillation or atrialflutter.

[0019] In achieving these objectives, the invention provides anelectrode support structure comprising a guide body having at its distalend a flexible spline leg. The spline leg is flexed to define an arcuateshape to facilitate intimate contact against tissue. An electrodeelement is carried by the spline leg for movement along its axis. Thestructure includes a control element coupled to the electrode element.The control element remotely imparts force to move the electrode elementalong the axis of the spline leg. Therefore, in use, the physician cancause the electrode element to travel along a path that the spline legdefines, without otherwise changing the location of the guide body.

[0020] The invention also provides a method for ablating tissue in aheart. The method introduces a probe into the heart. The probe carriesat least one elongated spline leg flexed outward of the probe to definean arcuate shape. The probe also includes at least one ablationelectrode that is movable along the at least one spline leg spline inresponse to the application of force. The method establishes contactbetween the ablation electrode and a region of heart tissue, along whichthe spline leg defines an elongated path. The method transmits ablationenergy to the ablation electrode while in contact with the tissueregion. The method also applies force to move the ablation electrodealong the at least one spline leg, while maintaining contact with thetissue, to ablate tissue along the elongated path.

[0021] Other features and advantages of the inventions are set forth inthe following Description and Drawings, as well as in the appendedClaims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a plan view of an ablation probe having a full-loopstructure for supporting multiple ablation elements;

[0023]FIG. 2 is an elevation view of a spline used to form the loopstructure shown in FIG. 1;

[0024]FIG. 3 is an elevation view of the distal hub used to form theloop structure shown in FIG. 1;

[0025]FIG. 4 is a side section view of the hub shown in FIG. 3;

[0026]FIG. 5 is a perspective, partially exploded view of the spline,distal hub, and base assembly used to form the loop structure shown inFIG. 1;

[0027]FIG. 6A is an enlarged perspective view of the base assembly shownin FIG. 5;

[0028]FIG. 6B is a side section view of an alternative base assembly forthe loop structure shown in FIG. 1;

[0029]FIG. 7 is an elevation view of a half-loop structure forsupporting multiple electrodes;

[0030]FIG. 8 is an elevation view of a composite loop structure forsupporting multiple electrodes comprising two circumferentially spacedhalf-loop structures;

[0031]FIG. 9 is an elevation view of a composite loop structurecomprising two full-loop structures positioned ninety degrees apart;

[0032]FIG. 10 is an elevation view, with parts broken away, of multipleelectrode elements comprising segmented rings carried by a loop supportstructure;

[0033]FIG. 11A is an enlarged view, with parts broken away, of multipleelectrode elements comprising wrapped coils carried by a loop supportstructure;

[0034]FIG. 11B is an elevation view, with parts broken away, of multipleelectrode elements comprising wrapped coils carried by a loop supportstructure;

[0035]FIG. 12 is a top view of a steering mechanism used to deflect thedistal end of the probe shown in FIG. 1;

[0036]FIG. 13 is a plan view of a full-loop structure for supportingmultiple electrode elements having an associated center stylet attachedto a remote control knob for movement to extend and distend thefull-loop structure;

[0037]FIG. 14 is a side section view of the remote control knob for thecenter stylet shown in FIG. 13;

[0038]FIG. 15 is a plan view of the full-loop structure shown in FIG.13, with the control knob moved to extend the full-loop structure;

[0039]FIG. 16 is a plan view of a full-loop structure shown in FIG. 13,with the control handle moves to distend the full-loop structure;

[0040]FIG. 17 is a plan view of a half-loop structure for supportingmultiple electrode elements having an associated center stylet attachedto a remote control knob for movement to extend and distend thehalf-loop structure;

[0041]FIG. 18 is a plan view of the half-loop structure shown in FIG.17, with the control knob moved to extend the half-loop structure;

[0042]FIG. 19 is a plan view of a half-loop structure shown in FIG. 17,with the control handle moves to distend the half-loop structure;

[0043]FIG. 20 is a plan view of a full-loop structure for supportingmultiple electrode elements having an associated center stylet attachedto a remote control knob for movement to extend and distend thefull-loop structure, and also having a remotely controlled steeringmechanism to flex the center stylet to bend the full-loop structure intoa curvilinear shape;

[0044]FIG. 21 is a side elevation view of the full-loop structure shownin FIG. 20;

[0045]FIG. 22 is an enlarged sectional view, generally taken along line22-22 in FIG. 20, showing the steering wires attached to the centerstylet to flex it;

[0046]FIGS. 23A and 23B are side elevation views showing the operationof the steering mechanism in bending the full-loop structure,respectively, to the left and to the right;

[0047]FIG. 24 is a largely diagrammatic, perspective view of thefull-loop structure bent to the right, as also shown in side elevationin FIG. 23B;

[0048]FIG. 25 is a plan view of the full-loop structure shown in FIG. 20and the associated remote control knob for extending and distending aswell as bending the full-loop structure;

[0049]FIG. 26 is a side section view, taken generally along lines 26-26in FIG. 25, of the control knob for extending and distending as well asbending the full-loop structure;

[0050]FIG. 27 is a largely diagrammatic, perspective view of thefull-loop structure when distended and bent to the right;

[0051]FIG. 28 is a largely diagrammatic, perspective view of a half-loopstructure with steerable center stylet bent to the right;

[0052]FIG. 29 is a plan, partially diagrammatic, view of a full-loopstructure for supporting multiple electrode elements having a movablespline leg attached to a remote control knob for movement to extend anddistend the full-loop structure;

[0053]FIG. 30A is a section view, taken generally along line 30A-30A inFIG. 29, of the interior of the catheter body lumen, through which themovable spline leg passes;

[0054]FIG. 30B is a side section view of an alternative way of securingthe full-loop structure shown in FIG. 29 to the distal end of thecatheter tube;

[0055]FIG. 31 is a plan, partially diagrammatic view of the full-loopstructure shown in FIG. 29 being extended by pulling the movable splineleg inward;

[0056]FIGS. 32 and 33 are plan, partially diagrammatic views of thefull-loop structure shown in FIG. 29 being distended by pushing themovable spline leg outward;

[0057]FIGS. 34 and 35 are largely diagrammatic views of the full-loopstructure shown in FIG. 29 being distended by pushing the movable splineleg outward while deployed in the atrium of a heart;

[0058]FIGS. 36, 37, and 38 are plan, partially diagrammatic views of afull-loop structure for supporting multiple electrode elements havingtwo movable spline legs attached to remote control knobs for coordinatedmovement to extend and distend the full-loop structure;

[0059]FIG. 39A is a plan view of a full-loop structure for supportmultiple electrode elements having a smaller, secondary loop structureformed in one spline leg;

[0060]FIG. 39B is a side view of the full-loop structure shown in FIG.39A, showing the smaller, secondary loop structure;

[0061]FIG. 40A is a perspective view of a modified full-loop structurefor supporting multiple electrode elements having an odd number of threeor more spline legs;

[0062]FIG. 40B is a top section view of the base of the full-loopstructure shown in FIG. 40A;

[0063]FIGS. 41, 42, and 43 are plan, partially diagrammatic, views of abifurcated full-loop structure for supporting multiple electrodeelements having movable half-loop structures to extend and distend thebifurcated full-loop structure;

[0064]FIGS. 44 and 45 are plan, partially diagrammatic, views of analternative form of a bifurcated full-loop structure for supportingmultiple electrode elements having movable center ring to extend anddistend the bifurcated full-loop structure;

[0065]FIG. 46 is a plan, partially diagrammatic, views of an alternativeform of a bifurcated full-loop structure for supporting multipleelectrode elements having both a movable center ring and movable splinelegs to extend and distend the bifurcated full-loop structure;

[0066]FIGS. 47, 48, and 49 are plan, partially diagrammatic, views ofanother alternative form of a bifurcated full-loop structure forsupporting multiple electrode elements having movable half-loopstructures to extend and distend the bifurcated full-loop structure;

[0067]FIG. 50 is a plan view of a full-loop structure for supporting andguiding a movable electrode element;

[0068]FIG. 51 is a side elevation view of the full-loop structure andmovable electrode element shown in FIG. 50;

[0069]FIG. 52 is an enlarged view of the movable electrode supported andguided by the structure shown in FIG. 50, comprising wound coils wrappedabout a core body;

[0070]FIG. 53 is an enlarged view of another movable electrode that canbe supported and guided by the structure shown in FIG. 50, comprisingbipolar pairs of electrodes;

[0071]FIG. 54 is a largely diagrammatic view of the full-loop structureand movable electrode element shown in FIG. 50 in use within the atriumof a heart;

[0072]FIG. 55 is a perspective, elevation view of a bundled loopstructure for supporting multiple electrode elements, comprising anarray of individual spline legs structures, each having a movableportion that independently extends and distends the individualstructures to shape and flex the overall bundled loop structure;

[0073]FIG. 56 is a top view of the bundled loop structure shown in FIG.55;

[0074]FIG. 57 is a perspective elevation view of the bundled loopstructure shown in FIG. 55 with some of the independently movable splinelegs extended and distended to change the flexure of the bundled loopstructure;

[0075]FIG. 58 is a top view of the bundled loop structure shown in FIG.57;

[0076]FIGS. 59A and 59B are, respectively, top and side views of abundled loop structure like that shown in FIG. 55 in position within anatrium, out of contact with the surrounding atrial wall;

[0077]FIGS. 60A and 60B are, respectively, top and side views of abundled loop structure like that shown in FIG. 57, with some of theindependently movable spline legs extended and distended to change theflexure of the bundled loop structure, to bring it into contact with thesurrounding atrial wall; and

[0078]FIG. 61 is a top section view of the base of the bundled loopstructure shown in FIG. 55.

[0079] The invention may be embodied in several forms without departingfrom its spirit or essential characteristics. The scope of the inventionis defined in the appended claims, rather than in the specificdescription preceding them. All embodiments that fall within the meaningand range of equivalency of the claims are therefore intended to beembraced by the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0080] This Specification discloses multiple electrode structures thatembody aspects the invention. This Specification also discloses tissueablation systems and techniques using multiple temperature sensingelements that embody other aspects of the invention. The illustrated andpreferred embodiments discuss these structures, systems, and techniquesin the context of catheter-based cardiac ablation. That is because thesestructures, systems, and techniques are well suited for use in the fieldof cardiac ablation.

[0081] Still, it should be appreciated that the invention is applicablefor use in other tissue ablation applications. For example, the variousaspects of the invention have application in procedures for ablatingtissue in the prostrate, brain, gall bladder, uterus, and other regionsof the body, using systems that are not necessarily catheter-based.

[0082] I. Loop Support Structures for Multiple Electrodes

[0083]FIG. 1 shows a multiple electrode probe 10 that includes a loopstructure 20 carrying multiple electrode elements 28.

[0084] The probe 10 includes a flexible catheter tube 12 with a proximalend 14 and a distal end 16. The proximal end 14 carries an attachedhandle 18. The distal end 16 carries a loop structure 20 that supportsmultiple electrodes.

[0085] In FIG. 1, the loop support structure 20 comprises two flexiblespline legs 22 spaced diametrically opposite each other. The dual legloop structure 20 shown in FIG. 1 will be called a “full-loop”structure.

[0086] The far ends of the spline legs 22 radiate from a distal hub 24.The near ends of the spline legs 22 radiate from a base 26 attached tothe distal end 16 of the catheter tube 12. The multiple electrodeelements 28 are arranged along each spline leg 22.

[0087] In one implementation, the two spline legs 22 of the structure 20are paired together in an integral loop body 42 (see FIG. 2). Each body42 includes a mid-section 44 from which the spline elements 22 extend asan opposed pair of legs. As FIG. 2 shows, the mid-section 44 includes apreformed notch or detent 46, whose function will be described later.

[0088] The loop body 42 is preferably made from resilient, inert wire,like Nickel Titanium (commercially available as Nitinol material).However, resilient injection molded inert plastic or stainless steel canalso be used. Preferably, the spline legs 22 comprise thin, rectilinearstrips of resilient metal or plastic material. Still, other crosssectional configurations can be used.

[0089] In this implementation (see FIGS. 3 and 4), the distal hub 24 hasa generally cylindrical side wall 50 and a rounded end wall 52. Alongitudinal slot 56 extends through the hub 24, diametrically acrossthe center bore 54.

[0090] In the illustrated embodiment, the hub 24 is made of an inert,machined metal, like stainless steel. The bore 54 and slot 56 can beformed by conventional EDM techniques. Still, inert molded plasticmaterials can be used to form the hub 24 and associated openings.

[0091] In this implementation, to assemble the structure 20 (see FIGS. 4and 5), a spline leg 22 of the hoop-like body 42 is inserted through theslot 56 until the mid-body section 44 enters the bore 54. The detent 46snaps into the bore 54 (see FIG. 4) to lock the body 42 to the hub 24,with the opposed pair of spline legs 22 on the body 42 radiating free ofthe slot 56 (see FIG. 5).

[0092] In the illustrated embodiment (see FIGS. 5 and 6A), the base 26includes an anchor member 62′ and a mating lock ring 64. The anchormember 62 fits with an interference friction fit into the distal end 16of the catheter tube 12. The lock ring 64 includes a series ofcircumferentially spaced grooves 66 into which the free ends of thespline legs 22 fit. The lock ring 64 fits about the anchor member 62 tocapture with an interference fit the free ends of the spline legs 22between the interior surface of the grooves 66 and the outer surface ofthe anchor member 62 (see FIG. 6). The anchor member 62/lock ring 64assembly holds the spline elements 22 in a desired flexed condition.

[0093] In an alternative construction (see FIG. 6B), the base 26 cancomprise a slotted anchor 63 carried by the distal end 16 of thecatheter tube 12. The slotted anchor 63 is made of an inert machinedmetal or molded plastic material. The slotted anchor 63 includes anouter ring 65 and a concentric slotted inner wall 67. The interior ofthe anchor 63 defines an open lumen 226 to accommodate passage of wiresand the like between the catheter tube bore 36 and the support structure20 (as will be described in greater detail later).

[0094] The inner wall 67 includes horizontal and vertical slots 69 and71 for receiving the free ends of the spline legs 22. The free ends passthrough the horizontal slots 69 and are doubled back upon themselves andwedged within the vertical slots 71 between the outer ring 65 and theinner wall 67, thereby securing the spline legs 22 to the anchor 63.

[0095] There are other alternative ways of securing the spline legs 22to the distal end 16 of the catheter tube 12, which will be describedlater.

[0096] Preferably, the full-loop structure 20 shown in FIG. 1 does notinclude a hub 24 like that shown in FIGS. 1 and 3, and, in addition,does not incorporate a detented integral loop body 42 like that shown inFIG. 2. Any single full-loop structure without a center stiffener orstylet (as will be described later) preferably comprises a single lengthof resilient inert wire (like Nickel Titanium) bent back upon itself andpreformed with resilient memory to form the desired full loop shape.Structure 112 in FIG. 29 (which will be described in greater detaillater) exemplifies the use of a preshaped doubled-back wire to form aloop, without the use of a hub 24 or detented loop body 42. FIGS. 10 and11B also show a portion of the doubled-back wire embodiment, free of thehub 24.

[0097]FIG. 7 shows an alternative loop structure 20(1) that includes asingle spline leg 22(1) carrying multiple electrode elements 28. Thissingle leg loop structure will be called a “half-loop” structure, incontrast to the dual leg loop structure 20 (i.e., the “full-loopstructure) shown in FIG. 1.

[0098] In assembling the half-loop structure 20(1) shown in FIG. 7, thehoop-like body 42 shown in FIG. 2 is cut on one side of the detent 46 toform the single spline leg 22(1). The single spline leg 22(1) issnap-fitted into the hub 24 and captured with an interference fit by theanchor member 62/lock ring 64 assembly of the base 26 in the manner justdescribed (shown in FIGS. 5 and 6A). Alternatively, the single splineleg 22(1) can be wedged within the base anchor ring 63 shown in FIG. 6B.In FIG. 7, the half-loop structure 20(1) also includes a centerstiffener 40 secured to the base 26 and to the bore 54 of the hub 24.The stiffener 40 can be made of a flexible plastic like Fortron, or froma hollow tube like hypo-tubing or braid plastic tubing.

[0099] It should be appreciated that other loop-type configurationsbesides the full-loop structure 20 and half-loop structure 20(1) arepossible. For example, two half-loop structures 20(1), one or bothcarrying electrode elements 28, can be situated in circumferentiallyspaced apart positions with a center stiffener 40, as FIG. 8 shows. Asanother example, four half-loop structures, or two full-loop structurescan be assembled to form a three-dimensional, basket-like structure 60(without using a center stiffener 40), like that shown in FIG. 9.

[0100] Regardless of the configuration, the loop structure provides theresilient support necessary to establish and maintain contact betweenthe electrode elements 28 and tissue within the body.

[0101] The electrode elements 28 can serve different purposes. Forexample, the electrode elements 28 can be used to sense electricalevents in heart tissue. In the illustrated and preferred embodiments,the principal use of the electrode elements 28 is to emit electricalenergy to ablate tissue. In the preferred embodiments, the electrodeelements 28 are conditioned to emit electromagnetic radio frequencyenergy.

[0102] The electrode elements 28 can be assembled in various ways.

[0103] In one preferred embodiment (see FIG. 10), the elements comprisemultiple, generally rigid electrode elements 30 arranged in a spacedapart, segmented relationship upon a flexible, electricallynonconductive sleeve 32 which surrounds the underlying spline leg 22.The sleeve 32 is made a polymeric, electrically nonconductive material,like polyethylene or polyurethane.

[0104] The segmented electrodes 30 comprise solid rings of conductivematerial, like platinum. The electrode rings 30 are pressure fittedabout the sleeve 32. The flexible portions of the sleeve 32 between therings 30 comprise electrically nonconductive regions. Alternatively, theelectrode segments 30 can comprise a conductive material, likeplatinum-iridium or gold, coated upon the sleeve 32 using conventionalcoating techniques or an ion beam assisted deposition (IBAD) process.For better adherence, an undercoating of nickel or titanium can beapplied. The electrode coating can be applied either as discrete,closely spaced segments or in a single elongated section.

[0105] In a more preferred embodiment (see FIGS. 11A and 11B), spacedapart lengths of closely wound, spiral coils are wrapped about thesleeve 32 to form an array of segmented, generally flexible electrodes34. The coil electrodes 34 are made of electrically conducting material,like copper alloy, platinum, or stainless steel. The electricallyconducting material of the coil electrode 34 can be further coated withplatinum-iridium or gold to improve its conduction properties andbiocompatibility.

[0106] The inherent flexible nature of a coiled electrode structures 34also makes possible the construction of a continuous flexible ablatingelement comprising an elongated, closely wound, spiral coil ofelectrically conducting material, like copper alloy, platinum, orstainless steel, wrapped about all or a substantial length of theflexible sleeve 32.

[0107] The electrode elements 28 can be present on all spline legs 22,as FIG. 1 shows, or merely on a selected number of the spline legs 22,with the remaining spline legs serving to add structural strength andintegrity to the structure.

[0108] The electrode elements 28 are electrically coupled to individualwires 58 (see FIG. 11A) to conduct ablating energy to them. The wires 58extend along the associated spline leg 22 (as FIG. 11A shows), through asuitable access opening provided in the base 24 (for example, the anchorlumen 226 shown in FIG. 6B) into and through the catheter body lumen 36(as generally shown in FIG. 1 and FIGS. 30A/B), and into the handle 18,where they are electrically coupled to external connectors 38 (see FIG.1). The connectors 38 plug into a source of RF ablation energy (notshown).

[0109] Various access techniques can be used to introduce the probe 10and its loop support structure 20 into the desired region of the heart.For example, to enter the right atrium, the physician can direct theprobe 10 through a conventional vascular introducer through the femoralvein. For entry into the left atrium, the physician can direct the probe10 through a conventional vascular introducer retrograde through theaortic and mitral valves.

[0110] Alternatively, the physician can use the delivery system shown inpending U.S. application Ser. No. 08/033,641, filed Mar. 16, 1993, andentitled “Systems and Methods Using Guide Sheaths for Introducing,Deploying, and Stabilizing Cardiac Mapping and Ablation Probes.”

[0111] In use, the physician verifies contact between the electrodeelements 28 and heart tissue using conventional pacing and sensingtechniques. Once the physician establishes contact with tissue in thedesired heart region, the physician applies ablating energy to theelectrode elements 28.

[0112] The electrode elements 28 can be operated in a uni-polar mode, inwhich the ablation energy emitted by the electrode elements 28 isreturned through an indifferent patch electrode attached to the skin ofthe patient (not shown). Alternatively, the elements 28 can be operatedin a bi-polar mode, in which ablation energy emitted by one element 28is returned through another element 28 on the spline leg 22.

[0113] The size and spacing of the electrode elements 28 shown in FIGS.10 and 11A/B are well suited for creating continuous, long and thinlesion patterns in tissue when ablation energy is applied simultaneouslyto adjacent emitting electrode elements 28. Continuous lesion patternsuniformly result when adjacent electrode elements 28 (i.e., the segments30 or coils 34) are spaced no farther than about 2.5 times the electrodesegment diameter apart. Further details of the formation of continuous,long and thin lesion patterns are found in copending U.S. patentapplication Ser. No. 08/287,192, filed Aug. 8, 1994, entitled “Systemsand Methods for Forming Elongated Lesion Patterns in Body Tissue UsingStraight or Curvilinear Electrode Elements,” which is incorporatedherein by reference.

[0114] Using rigid electrode segments 30, the length of the eachelectrode segment can vary from about 2 mm to about 10 mm. Usingmultiple rigid electrode segments longer than about 10 mm each adverselyeffects the overall flexibility of the element. Generally speaking,adjacent electrode segments 30 having lengths of less than about 2 mm donot consistently form the desired continuous lesion patterns.

[0115] When flexible electrode segments 34 are used, electrode segmentslonger that about 10 mm in length can be used. Flexible electrodesegments 34 can be as long as 50 mm. If desired, the flexible electrodestructure 34 can extend uninterrupted along the entire length of thesupport spline 22.

[0116] The diameter of the electrode segments 30 or 34 and underlyingspline leg 22 (including the flexible sleeve 32) can vary from about 2French to about 10 French.

[0117] Preferably (as FIGS. 10 and 11B show), the side of the ablationelements 28 that, in use, is exposed to the blood pool is preferablycovered with a coating 48 of an electrically and thermally insulatingmaterial. This coating 48 can be applied, for example, by brushing on aUV-type adhesive or by dipping in polytetrafluoroethylene (PTFE)material.

[0118] The coating 48 prevents the transmission of ablating energydirectly into the blood pool. Instead, the coating 48 directs theapplied ablating energy directly toward and into the tissue.

[0119] The focused application of ablating energy that the coating 48provides helps to control the characteristics of the lesion. The coating48 also minimizes the convective cooling effects of the blood pool uponthe ablation element while ablating energy is being applied, therebyfurther enhancing the efficiency of the lesion formation process.

[0120] In the illustrated and preferred embodiments (see FIGS. 10 and11A/B), each flexible ablation element carries at least one and,preferably, at least two, temperature sensing elements 68. The multipletemperature sensing elements 68 measure temperatures along the length ofthe electrode element 28. The temperature sensing elements 68 cancomprise thermistors or thermocouples.

[0121] An external temperature processing element (not shown) receivesand analyses the signals from the multiple temperature sensing elements68 in prescribed ways to govern the application of ablating energy tothe flexible ablation element. The ablating energy is applied tomaintain generally uniform temperature conditions along the length ofthe element.

[0122] Further details of the use of multiple temperature sensingelements in tissue ablation can be found in copending U.S. patentapplication Ser. No. 08/286,930, filed Aug. 8, 1994, entitled “Systemsand Methods for Controlling Tissue Ablation Using Multiple TemperatureSensing Elements.”

[0123] To aid in locating the structure 20 within the body, the handle16 and catheter body 12 preferably carry a steering mechanism 70 (seeFIGS. 1 and 12) for selectively bending or flexing the distal end 16 ofthe catheter body 12.

[0124] The steering mechanism 18 can vary. In the illustrated embodiment(see FIG. 12), the steering mechanism 70 includes a rotating cam wheel72 with an external steering lever 74 (see FIG. 1). As FIG. 12 shows,the cam wheel 72 holds the proximal ends of right and left steeringwires 76. The steering wires 76, like the signal wires 58, pass throughthe catheter body lumen 36. The steering wires 76 connect to the leftand right sides of a resilient bendable wire or spring (not shown)enclosed within the distal end 16 of the catheter body 12. Forwardmovement of the steering lever 74 flexes or curves the distal end 16down. Rearward movement of the steering lever 74 flexes or curves thedistal end 16 up.

[0125] Further details of this and other types of steering mechanismsare shown in Lundquist and Thompson U.S. Pat. No. 5,254,088, which isincorporated into this Specification by reference.

[0126] II. Variable Shape Loop Support Structures

[0127] To uniformly create long, thin lesions having the desiredtherapeutic effect, the loop support structure 20 or 20(1) must make andmaintain intimate contact between the electrode elements 28 and theendocardium.

[0128] The invention provides loop support structures that the physiciancan adjust to adapt to differing physiologic environments.

[0129] A. Distended Loop Structures

[0130] The adjustable loop structure 78 shown in FIG. 13 is in manyrespects similar to the full-loop structure 20 shown in FIG. 1. Theadjustable full-loop structure 78 includes the pair of diametricallyopposite spline legs 22 that radiate from the base 26 and hub 24.

[0131] In addition, the adjustable full-loop structure 78 includes aflexible stylet 80 attached at its distal end to the hub bore 54. Thestylet 80 can be made from a flexible plastic material, like Fortron, orfrom a hollow tube, like hypo-tubing or braid plastic tubing.

[0132] The stylet 80 extends along the axis of the structure 78, throughthe base 26 and catheter body lumen 36, and into the handle 18. In thisarrangement, the stylet 80 is free to slide fore and aft along the axisof the catheter body 12.

[0133] The proximal end of the stylet 80 attaches to a control knob 82in the handle 18 (as FIG. 13 shows). The control knob 82 moves within agroove 84 (see FIGS. 13 and 14) in the handle 18 to impart fore and aftmovement to the stylet 80. Stylet movement changes the flexure of thestructure 78.

[0134] Forward movement of the stylet 80 (i.e., toward the distal end16) pushes the hub 24 away from the base 26 (see FIG. 15). The loopstructure 78 elongates as the spline legs 22 straighten and moveradially inward, to the extent permitted by the resilience of the splinelegs 22. With the spline legs 22 straightened, the loop structure 78presents a relatively compact profile to facilitate vascularintroduction.

[0135] Rearward movement of the stylet 80 (i.e., toward the distal end16) pulls the hub 24 toward the base 26 (see FIG. 16). The spline legs22 bend inward in the vicinity of the hub 24, while the remainder of thesplines, constrained by the base, distend. The loop structure 78 bowsradially out to assume what can be called a “heart” shape.

[0136] When the structure 78 is positioned within the atrium 88 of aheart in the condition shown in FIG. 16, the stylet 80 compresses thespline legs 22, making them expand or bow radially. The expansionpresses the distended midportion of the spline legs 22 (and theelectrode elements 28 they carry) symmetrically against opposite walls86 of the atrium 88. The symmetric expansion of the outwardly bowedspline legs 22 presses the opposite atrial walls 86 apart (as FIG. 16shows), as the radial dimension of the loop structure 78 expands to spanthe atrium 88.

[0137] The symmetric expansion presses the electrode elements 28 intointimate surface contact against the endocardium. The symmetricexpansion stabilizes the position of the loop structure 78 within theatrium 88. The resilience of the spline legs 22, further compressed bythe pulled-back stylet 80, maintains intimate contact between theelectrode elements 28 and atrial tissue, without trauma, as the heartexpands and contracts.

[0138] As FIGS. 17 to 19 show, the push-pull stylet 80 can also be usedin association with a half-loop structure 90, like that previously shownand discussed in FIG. 7. In this arrangement, the movable stylet 80substitutes for the flexible, but otherwise fixed stiffener 40.

[0139] In this arrangement, pushing the stylet 80 forward (as FIG. 18shows) elongates the half-loop structure 90 for vascular introduction.Pulling the stylet 80 rearward (as FIG. 19 shows) bows the single splineleg 22 of the structure outward, expanding it so that more securecontact can be achieved against the atrial wall 86, or wherever tissuecontact is desired.

[0140] B. Curvilinear Loop Structures

[0141]FIGS. 20 and 21 show a full-loop structure 92 that includes acenter stylet 94, which can be flexed. The flexing of the center stylet94 bends the spline legs 22 in a second direction different than theradial direction in which they are normally flexed. In the illustratedembodiment, this second direction is generally perpendicular to the axesof the spline legs 22, as FIGS. 23A/B and 24 show, although acute bendsthat are not generally perpendicular can also be made. The bending ofthe spline legs 22 in this fashion makes possible the formation of long,thin curvilinear lesions using a full-loop structure 92, or (as will bedescribed later) in a half-loop structure 110, as well.

[0142] The stylet 94 itself can be either fixed in position between thehub 24 and the base 26, or movable along the axis of the loop structure92 to extend and distend the radial dimensions of the spline legs 22 inthe manner already described (see FIGS. 15 and 16). In the illustratedand preferred embodiment, the stylet 94 slides to alter the radialdimensions of the structure.

[0143] In one implementation, as FIG. 22 best shows, the stylet 94 ismade from a metal material, for example stainless steel 17-7, Elgiloy™material, or Nickel Titanium material. A pair of left and right steeringwires, respectively 96(R) and 96(L) is attached to opposite sidesurfaces of the stylet 94 near the hub 24, by adhesive, soldering, or bysuitable mechanical means. The steering wires 96(R) and 96(L) areattached to the stylet side surfaces in a diametric opposite orientationthat is at right angles to the radial orientation of the spline legs 22relative to the stylet 94.

[0144] The steering wires 96(R) and 96(L) extend along the stylet 94,through the base 26 and catheter body lumen 36, and into the handle 18(see FIG. 25). Preferable, as FIG. 22 best shows, a tube 98 surroundsthe stylet 94 and steering wires 96(R) and 96(L), at least along thedistal, exposed part of the stylet 94 within the structure 92, keepingthem in a close relationship. The tube 98 can be heat shrunk to fitclosely about the stylet 94 and steering wires 96(R) and 96(L).

[0145] As FIGS. 25 and 26 show, a groove 100 in the handle carries acontrol assembly 102. The stylet 94 is attached to the control assembly102, in the manner already described with respect to the control knob 82in FIGS. 13 and 14. Sliding movement of the control assembly 102 withinthe groove 100 imparts fore and aft movement to the stylet 94, therebydistending or extending the loop structure 92.

[0146] The control assembly 102 further includes a cam wheel 104 (seeFIG. 26) rotatable about an axle on the control assembly 102 in responseto force applied to an external steering lever 108. The cam wheel 104holds the proximal ends of the steering wires 96(R) and 96(L), in themanner disclosed in Lundquist and Thompson U.S. Pat. No. 5,254,088,already discussed, which is incorporated herein by reference.

[0147] Twisting the steering lever 108 counterclockwise applies tensionto the left steering wire 96(L), bending the loop structure 92 to theleft (as FIG. 23A shows). The electrode elements 28 (which in FIGS. 20to 27 comprises a continuous coil electrode 34, described earlier)likewise bend to the left.

[0148] Similarly, twisting the steering lever 108 clockwise appliestension to the right steering wire 96(R), bending the loop structure 92′to the right (as FIGS. 23B and 24 show). The electrode elements 28likewise bend to the right.

[0149] The bent electrode elements 28, conforming to the bent splinelegs 22, assume different curvilinear shapes, depending upon amount oftension applied by the steering wires 96(R) and 96(L). When contactingtissue, the bent electrode elements 28 form long, thin lesions incurvilinear patterns.

[0150] In an alternative implementation, the stylet 94 is not flexibleand remotely steerable, but is instead made of a malleable metalmaterial, like annealed stainless steel. In this arrangement, beforedeployment in the body, the physician applies external pressure tomanually bend the stylet 94 into a desired shape, thereby imparting adesired curvilinear shape to the electrode elements of the associatedloop structure. The malleable material of the stylet 94 retains thepreformed shape, until the associated loop structure is withdrawn fromthe body and sufficient external pressure is again applied by thephysician to alter the stylet shape.

[0151] In addition to having a malleable stylet 94, the splines 22themselves can also be made of a malleable material, like annealedstainless steel, or untreated stainless steel 17-7, or untreated NickelTitanium. In one implementation, the most distal parts of the malleablesplines 22 are heat treated to maintain their shape and not collapseduring introduction and deployment in the vascular system. This willalso give the overall structure greater stiffness for better contactwith the tissue. It also gives the physician the opportunity to bend thestructure to form long, thin, lesions in prescribed curvilinear patternsset by the malleable splines.

[0152] Whether flexible and remotely flexed during deployment, ormalleable and manually flexed before deployment, by further adjustingthe fore-and-aft position of the stylet 94, the physician can alsocontrol the radial dimensions of the loop structure 94 in concert withcontrolling the curvilinear shape of the loop structure 92, as FIG. 27shows. A diverse array of radial sizes and curvilinear shapes is therebyavailable.

[0153] As FIG. 28 shows, a half-loop structure 110 can also include afixed or movable stylet 94 with steering wires 96(R) and 96(L). The useof the same handle-mounted control assembly 102/rotatable cam 104assembly shown in FIGS. 25 and 26 in association with the half-loopstructure 110 makes possible the creation of diverse curvilinear shapesof variable radii. Alternatively, a malleable stylet 94 and malleablesplines can be used.

[0154] C. Loop Structures with Movable Spline Legs

[0155] FIGS. 29 to 35 show a full-loop structure 112 in which only onespline leg 114 is attached to the base 26. The fixed spline leg 114 ispreformed with resilient memory to assume a curve of a selected maximumradius (shown in FIG. 33). The other spline leg 116, locateddiametrically opposed to the fixed spline leg 114,, extends through thebase 26 and catheter body lumen 36 (see FIGS. 30A and 30B) into thehandle 18. The spline leg 116 slides fore and aft with respect to thebase 26. Movement of the spline leg 116 changes the flexure of thestructure 112.

[0156] The full-loop structure 112 shown in FIGS. 29 to 35 need notinclude a hub 24 like that shown in FIGS. 1 and 3, and, in addition,need not incorporate a detented integral loop body 42 like that shown inFIG. 2. Any single full-loop structure without a center stiffener orstylet, like the structure 112 in FIG. 29, can comprise a single lengthof wire bent back upon itself and preformed with resilient memory toform the desired full loop shape. For the same reason, the singlefull-loop structure 20 shown in FIG. 1 can, in an alternativeconstruction, be made without a hub 24 and a detented loop body 42, andinstead employ a preshaped doubled-back wire to form a loop, like thestructure 20.

[0157]FIG. 30B shows an alternative way of securing the fixed spline leg114 to the distal end 16 of the catheter tube 12, without using a base26. In this embodiment, the free end of the fixed spline leg 114 liesagainst the interior of the tube 12. The leg 114 passes through a slit115 formed in the catheter tube 12. The leg 114 is bent back upon itselfin a u-shape to lie against the exterior of the tube 12, wedging thetube 12 within the u-shape bend 117. A sleeve 119 is heat shrunk aboutthe exterior of the tube 12 over the region where the u-shape bend 117of the spline leg 114 lies, securing it to the tube 12. Alternatively, ametallic ring (not shown) can be used to secure the spline leg 114 tothe tube 12. The movable spline leg 116 and wires 58 pass through theinterior bore 36 of the catheter tube 12, as before described.

[0158] The proximal end of the spline leg 116 (see FIG. 29) is attachedto a movable control knob 82 carried in a groove 84 on the handle 18,like that shown in FIG. 13. Movement of the control knob 82 within thegroove 84 thereby imparts fore-and-aft movement to the spline leg 116.

[0159] In the illustrated embodiment, the fixed spline leg 114 carrieselectrode elements 28 in the manner already described. The movablespline leg 116 is free of electrode elements 28. Still, it should beappreciated that the movable spline leg 116 could carry one or moreelectrode elements 28, too.

[0160] As FIGS. 31 to 33 show, moving the control knob 82 forward slidesthe movable spline leg 116 outward, and vice versa. The movable splineleg 116 applies a counter force against the resilient memory of thefixed spline leg 114, changing the flexure and shape of the loopstructure 112 for vascular introduction and deployment in contact withtissue. By pulling the movable spline leg 116 inward (as FIG. 31 shows),the counter force contracts the radius of curvature of the fixed splineleg 114 against its resilient memory. Pushing the movable spline leg 116outward (as FIGS. 32 and 33 show) allows the resilient memory of thefixed spline leg 114 to expand the radius of curvature until theselected maximum radius is achieved. The counter force applied changesthe flexure and shapes the fixed spline leg 114 and the electrodeelements 28 it carries to establish and maintain more secure, intimatecontact against atrial tissue.

[0161] The magnitude (designated V in FIGS. 31 to 33) of the counterforce, and the resulting flexure and shape of the loop structure 112,varies according to extent of outward extension of the movable splineleg 116. Pulling the movable spline leg 116 progressively inward(thereby shortening its exposed length) (as FIG. 31 shows) contracts theloop structure 112, lessening its diameter and directing the counterforce progressively toward the distal end of the structure. Pushing themovable spline leg 116 progressively outward (thereby lengthening itsexposed length) (as FIGS. 32 and 33 show) progressively expands the loopstructure 112 in response to the resilient memory of the fixed splineleg 114, increasing its diameter and directing the counter forceprogressively away from the distal end of the structure.

[0162] As FIGS. 34 and 35 show, by manipulating the movable spline leg116, the physician can adjust the flexure and shape of the loopstructure 112 within the atrium 88 from one that fails to makesufficient surface contact between the electrode element 28 and theatrial wall 86 (as FIG. 34 shows) to one that creates an extended regionof surface contact with the atrial wall 86 (as FIG. 35 shows).

[0163] FIGS. 36 to 38 show a full-loop structure 118 in which eachspline leg 120 and 122 is independently movable fore and aft withrespect to the base 26. In the illustrated embodiment, both spline legs120 and 122 carry electrode elements 28 in the manner already described.

[0164] In this arrangement, the handle 18 includes two independentlyoperable, sliding control knobs 124 and 126 (shown diagrammatically inFIGS. 36 to 38), each one attached to a movable spline leg 120/122, toimpart independent movement to the spline legs 120/122 (as shown byarrows in FIGS. 36 to 38). Each spline leg 120/122 is preformed withresilient memory to achieve a desired radius of curvature, therebyimparting a resilient curvature or shape to the full-loop structure 118itself. Coordinated opposed movement of both spline legs 120/122 (asFIGS. 37 and 38 show) using the control knobs 124/126 allows thephysician to elongate the curvature of the loop structure 118 into moreof an oval shape, compared to more circular loop structures 112 formedusing a single movable leg 116, as FIGS. 31 to 33 show.

[0165]FIGS. 39A and 39B show an alternative full-loop structure 128having one spline leg 130 that is fixed to the base 26 and anotherspline leg 132, located diametrically opposed to the fixed spline 130,that is movable fore and aft with respect to the base 26 in the manneralready described. The movable spline leg 132 can carry electrodeelements 28 (as FIG. 39A shows), or be free of electrode elements,depending upon the preference of the physician.

[0166] In the structure shown in FIGS. 39A and 39B, the fixed spline leg130 branches in its midportion to form a smaller, secondary full-loopstructure 134 that carries electrode elements 28. In the embodimentshown in FIGS. 39A and 39B, the secondary loop structure 134 lies in aplane that is generally perpendicular to the plane of the main full-loopstructure 128.

[0167] The smaller, secondary full-loop structure 134 makes possible theformation of annular or circumferential lesion patterns encircling, forexample, accessory pathways, atrial appendages, and the pulmonary veinwithin the heart. In the illustrated embodiment, the movable spline leg132 compresses the secondary full-loop structure 134, urging andmaintaining it in intimate contact with the targeted tissue area.

[0168]FIGS. 39A and 39B therefore show a compound flexible support forelectrode elements. While the primary support structure 128 and thesecondary support structure 134 are shown as full loops, it should beappreciated that other arcuate or non-arcuate shapes can be incorporatedinto a compound structure. The compound primary structure 128 integratedwith a secondary structure 134 need not include a movable spline leg,or, if desired, both spline legs can be movable. Furthermore, a centerstylet to contract and distend the main structure 128 can also beincorporated, with or without a stylet steering mechanism.

[0169]FIGS. 40A and B show a modified full-loop structure 216 having anodd number of spline legs 218, 220, and 222. The structure 216 includestwo spline legs 218 and 220 that, in the illustrated embodiment, arefixed to the base 26 about 120° apart from each other. As FIG. 40Bshows, the base 26 is generally like that shown in FIG. 6B, with theslotted anchor 63 in which the near ends of the legs 218 and 220 aredoubled back and wedged. The structure 216 also includes a third splineleg 222 that, in the illustrated embodiment, is spaced about 120° fromthe fixed spline legs 218/220. As FIG. 40B shows, the near end of thethird spline leg 222 is not attached to the base 26, but passes throughthe inner lumen 226 into the lumen 36 of the catheter tube 12. The thirdspline leg 222 is thereby movable fore and aft with respect to the base26 in the manner already described. Alternatively, all spline legs 218,220, and 222 can be fixed to the base 26, or more than one spline legcan be made moveable.

[0170] A hub 24 like that shown in FIGS. 3 and 4 includescircumferentially spaced slots 56 to accommodate the attachment of thethree splines 218, 220, and 222.

[0171] The fixed splines 218 and 220 carry electrode elements 28 (asFIG. 40A shows), while the movable spline 22 is free of electrodeelements. As FIG. 40B show, the wires 58 coupled to the electrodeelements 28 pass through the anchor lumen 226 for transit through thecatheter tube bore 36. The orientation of the fixed splines 218 and 220relative to the movable spline 222 thereby presents an ablation loop224, like the secondary loop structure 134 shown in FIGS. 39A/B, thatlies in a plane that is generally transverse of the plane of the movablespline 222. Of course, other orientations of an odd number of three ormore spline legs can be used.

[0172] The movable spline leg 222 extends and compresses the secondarystructure 134 to urge and maintain it in intimate contact with thetargeted tissue area. Of course, a center stylet to further contract anddistend the ablation loop 224 can also be incorporated, with or withouta stylet steering mechanism.

[0173] D. Bifurcated Loop Structures

[0174]FIGS. 41, 42, and 43 show a variation of a loop structure,which-will be called a bifurcated full-loop structure 136. The structure136 (see FIG. 41) includes two oppositely spaced splines legs 138 and140, each carrying one or more electrode elements 28. The near end ofeach spline leg 138/140 is attached to the base 26. The far end of eachspline leg 138/140 is attached a stylet 142 and 144. Each spline leg138/140 is preformed with resilient memory to achieve a desired maximumradius of curvature (which FIG. 41 shows).

[0175] The spline leg stylets 142/144 are joined through a junction 146to a common control stylet 148. The common control stylet 148 passesthrough the catheter body lumen 36 to a suitable slidable control knob150 in the handle 18, as already described. By sliding, the control knob150 moves the control stylet 148 to change the flexure of the splinelegs 138/140.

[0176] When the control stylet 148 is fully withdrawn, as FIG. 41 shows,the junction 146 is located near the base 26 of the structure 136, andthe spline legs 138/140 assume their preformed maximum radii ofcurvatures. The spline legs 138/140 form individual half-loop structures(like shown in FIG. 7) that together emulate a full-loop structure (likethat shown in FIG. 1), except for the presence of a connecting, distalhub 24.

[0177] Forward movement of the control stylet 148 first moves thejunction 146 within the confines of the structure 136, as FIG. 42 shows.The forward movement of the control stylet 148 is translated by thespline leg stylets 142/144 to urge the spline legs 138/140 apart. Thedistal end of the bifurcated structure 136 opens like a clam shell.

[0178] As the spline legs 138/140 separate, they distend. The controlstylet 150 thus compresses the splines legs 138/140 to press them intocontact with the tissue area along opposite sides of the structure 136.In this way, the bifurcated structure 136 emulates the full-loopstructure 78, when distended (as FIG. 16 shows).

[0179] Continued forward movement of the control stylet 150 (as FIG. 43shows) moves the junction 146 and attached spline leg stylets 142/146out beyond the confines of the structure 136. This continued forwardmovement extends the spline legs 136/140, while moving them radiallyinward. This, in effect, collapses the bifurcated structure 136 into arelatively low profile configuration for vascular introduction. In thisway, the bifurcated structure 136 emulates the full-loop structure 78,when elongated (as FIG. 15 shows).

[0180]FIGS. 44 and 45 show an alternative embodiment of a bifurcatedfull-loop structure 152. The structure 152 includes two oppositelyspaced spline legs 154/156, each carrying one or more electrode elements28, like the structure 136 shown in FIGS. 41 to 43. Each spline leg154/156 is preformed with a resilient memory to assume a desired maximumradius of curvature (which FIG. 44 shows).

[0181] Unlike the structure 136 shown in FIGS. 41 to 43, the structure152 shown in FIGS. 44 and 45 fixes both ends of the spline legs 154/156to the base 26. The spline legs 154/156 thereby form stationary,side-by-side half-loop structures, each with an inner portion 158 and anouter portion 160. Together, the stationary half-loop structures createthe bifurcated full-loop structure 152.

[0182] In this arrangement, a center stylet 162 is attached to a ring164 that commonly encircles the inner portions 158 of the spline legs154/156 along the center of the structure 152. Movement of the stylet162 slides the ring 164 along the inner leg portions 158. The stylet 162passes through the catheter body lumen 36 to a suitable control in thehandle (not shown), as already described.

[0183] Forward movement of the ring 164 (as FIG. 45 shows) jointlyextends the spline legs 154/156, creating a low profile for vascularintroduction. Rearward movement of the ring 164 (as FIG. 44 shows)allows the resilient memory of the preformed spline legs 154/156 to bowthe legs 154/156 outward into the desired loop shape.

[0184]FIG. 46 shows another alternative embodiment of a bifurcatedfull-loop structure 166. This structure 166 has two oppositely spacedspline legs 168 and 170, each carrying one or more electrode elements28. Each spline leg 168/170 is preformed with a resilient memory toassume a maximum radius of curvature (which FIG. 46 shows).

[0185] The near end of each spline leg 168/170 is attached to the base26. The far end of each spline leg 168/170 is individually attached toits own stylet 172/174. Instead of joining a common junction (as in thestructure 136 shown in FIGS. 41 to 43), the spline stylets 172/174 ofthe structure 166 individually pass through the catheter body lumen 36to suitable control knobs (not shown) in the handle 18. Like theembodiment shown in FIGS. 44 and 45, a third stylet 176 is attached to aring 178 that encircles the spline stylets 172 and 174. The third stylet176 passes through the guide tube lumen 36 to its own suitable controlknob (not shown) in the handle 18.

[0186] The embodiment shown in FIG. 46 allows the physician to move thering 178 up and down along the spline stylets 172 and 174 to shape andchange the flexure of the structure 166 in the manner shown in FIGS. 44and 45. Independent of this, the physician can also individually movethe spline stylets 172 and 174 to further shape and change the flexureof each spline leg 168 and 170, as in the case of the movable splinelegs 120/122 shown in FIGS. 36 to 38. This structure 166 thus gives thephysician latitude in shaping the loop structure to achieve the desiredcontact with the atrial wall.

[0187] Another alternative embodiment of a bifurcated full-loopstructure 180 is shown in FIGS. 47 to 49. In this embodiment, thestructure 180 includes two oppositely spaced spline legs 182 and 184,each carrying one or more electrode elements 28. Each spline leg 182/184is preformed with a resilient memory to assume a desired maximum radiusof curvature (which FIG. 49 shows).

[0188] The inner portion 186 of each spline leg 182/184 is attached tothe base 26. A stationary ring 190 encircles the inner portions 186 nearthe distal end of the structure 180, holding them together.

[0189] The outer portion 188 of each spline leg 182/184 is free ofattachment to the base 26 and is resiliently biased away from the base26. Each outer portion 188 is individually attached to its own stylet192 and 194. The spline stylets 192 and 194 individually pass throughthe catheter body lumen 36 to suitable control knobs (not shown) in thehandle 18.

[0190] Pulling the spline legs stylets 192/194 rearward pulls the outerportion 188 of the attached spline leg 182/184 radially toward the base26, against their resilient memories, creating a low profile suitablefor vascular access (as FIG. 47 shows). Pushing the spline stylets192/194 forward pushes the outer portion 188 of the attached spline leg182/184, aided by the resilient memory of the spline leg 182/184,outward (as FIGS. 48 and 49 show). The spline stylets 192/194 can bemanipulated together or individually to achieve the shape and flexuredesired.

[0191] E. Loop Support Structures for Movable Electrodes

[0192]FIGS. 50 and 51 show a full-loop structure 196 which supports amovable ablation element 198. The structure 196 includes a pair ofspline legs 200 secured at their distal ends to the hub 24 and at theirproximal ends to the base 26, in the manner described in associationwith the structure shown in FIG. 1. A center stiffener 202 extendsbetween the base 26 and the hub 24 to lend further strength.

[0193] The ablation element 198 (see FIG. 52) comprises a core body 204made of an electrically insulating material. The body 204 includes acentral lumen 26, through which one of the spline legs 200 passes. Thecore body 204 slides along the spline leg 200 (as shown by arrows inFIGS. 50 to 52).

[0194] In the illustrated and preferred embodiment (see FIG. 52), a coilelectrode element 34 (as already described) is wound about the core body204. Alternatively, the core body 204 can be coated with an electricallyconducting material or have an electrically conducting metal bandfastened to it. As shown in FIG. 53, the ablation element can alsocomprise a composite structure 198(1) (see FIG. 53) of two bi-polarelectrodes 208 separated by an electrically insulating material 210. Thecore body 204 of the electrode can range in diameter from 3 Fr to 8 Frand in length from 3 mm to 10 mm.

[0195] A guide wire 212 is attached to at least one end of the ablationelectrode 198 (see FIGS. 50 and 52). The guide wire 212 extends from thehandle 18 through the catheter body lumen 36, along the center stiffener202 and through the hub 24 for attachment to the ablation element 198. Asignal wire 214 also extends in common along the guide wire 212 (seeFIG. 52) to supply ablation energy to the electrode 198. The proximalend of the guide wire 212 is attached to a suitable control knob (notshown) in the handle 18. Movement of the guide wire 212 forward pushesthe ablation element 198 along the spline leg 200 from the distal end ofthe structure 196 to the proximal end.

[0196] Two guide wires (212 and 213) may be used (as FIG. 52 shows),which are attached to opposite ends of the ablation element 198. Pullingon one guide wire 212 advances the electrode 198 toward the distal endof the structure 196, while pulling on the other guide wire 213 advancesthe electrode 198 in the opposite direction toward the proximal end ofthe structure 196. In an alternative implementation (not shown), thedistal tip of a second catheter body can be detachably coupled eithermagnetically or mechanically to the movable electrode 198. In thisimplementation, the physician manipulates the distal end of the secondcatheter body into attachment with the electrode 198, and then uses thesecond catheter body to drag the electrode 198 along the structure 196.

[0197] In use (as FIG. 54 shows), once satisfactory contact has beenestablished with the atrial wall 86, sliding the ablation electrode 198along the spline leg 200 while applying ablation energy creates a longand thin lesion pattern. The ablation can be accomplished by eithermoving the electrode 198 sequentially to closely spaced locations andmaking a single lesion at each location, or by making one continuouslesion by dragging the electrode 198 along the tissue while ablating.

[0198] One or both spline legs 200 can also be movable with respect tothe base, as before described, to assure intimate contact between theablation element 198 and the endocardium.

[0199] F. Bundled Loop Structures

[0200] The invention makes possible the assembly of bundled,independently adjustable loop structures to form a dynamic threedimensional electrode support structure 228, like that shown in FIGS. 55to 58.

[0201] The structure 228 shown in FIGS. 55 to 58 comprises four splinelegs (designated L1, L2, L3, and L4) circumferentially spaced ninetydegrees apart. Each spline leg L1, L2, L3, and L4 is generally like thatshown in FIG. 29. Each leg L1, L2, L3, and L4 is preformed withresilient memory to assume a curve of selected maximum radius. In theillustrated embodiment, each leg L1 to L4 carries at least one electrodeelement 28, although one or more of the legs L1 to L4 could be free ofelectrode elements 28.

[0202] The outer portions 230 of each spline leg L1 to L4 are attachedto the structure base 26. As FIG. 61 shows, the base 26 is similar tothat shown in FIG. 26, having an outer ring 236 and a concentric slottedinner element 238, through which the near ends of the outer spline legportions 230 extend. The near ends are doubled back upon themselves andwedged in the space 240 between the outer ring 236 and inner element238, as earlier shown in FIG. 6B.

[0203] The inner portions 232 of each spline leg L1, L2, L3, and L4 arenot attached to the base 26. They pass through lumens 242 in the innerelement 238 of the base 26 (see FIG. 61) and into catheter body lumen 36for individual attachment to control knobs 234 on the handle 18 (seeFIG. 55). Wires 58 associated with the electrode elements 28 carried byeach leg L1 to L4 pass through other lumens 244 in the inner element 238(see FIG. 61).

[0204] The inner portion 232 of each spline leg L1 to L4 isindependently movable, in the same way as the spline leg shown in FIGS.31 to 35. By manipulating the control knobs 234, the physician canchange the normal flexure of the structure 228 (which FIGS. 55 and 56show) to a new flexure (which FIGS. 57 and 58 show), by altering theshape each spline leg L1 to L4 independent of each other. As FIGS. 57and 58 show, the inner portion 232 of leg L4 has been pulled aft,compressing the associated loop. The inner portion 232 of leg L2 hasbeen pushed forward, expanding the associated loop.

[0205] As FIGS. 59A/B and 60A/B show, by selective manipulation of themovable inner portions 232 of the spline legs L1 to L4, the physiciancan adjust the shape of the three dimensional loop structure 228 withinthe atrium 88 from one that fails to make sufficient surface contactbetween the electrode element 28 and the atrial wall 86 (as FIGS. 59A/Bshow) to one that expands the atrium 88 and creates an extended regionof surface contact with the atrial wall 86 (as FIGS. 60A/60B show). Thephysician can thereby tailor the shape of the three dimensionalstructure 228 to the particular physiology of the patient.

[0206] In an alternative arrangement, the inner portions 232 of thespline legs L1 to L4 can be fixed to the base 26 and the outer portions230 made free to move in the manner shown in FIGS. 47 to 49.

[0207] III. Conclusion

[0208] It should be now be apparent that one or more movable spline legscan be used in association with a movable center stylet to providecontrol of the shape and flexure of the ablation element. The furtherinclusion of steering wires on the movable stylet, or the use of amalleable stylet and/or malleable spline legs adds the ability to formcurvilinear lesion patterns.

[0209] It is thereby possible to combine in a single loop supportstructure one or more movable spline legs (as FIGS. 31 to 38 show), amovable center stylet (as FIGS. 13 to 19 show), and a stylet steeringassembly or malleable stylet/splines (as FIGS. 20 to 28 show). Such astructure is capable of creating a diverse number of shapes and contactforces to reliably achieve the type and degree of contact desiredbetween the ablation elements and the targeted tissue area, despitephysiologic differences among patients.

[0210] It should also be appreciated that the invention is applicablefor use in tissue ablation applications that are not catheter-based. Forexample, any of the loop structures like those described in thisapplication can be mounted at the end of hand-held probe for directplacement by the physician in contact with a targeted tissue area. Forexample, a hand held loop structure carrying multiple electrodes can bemanipulated by a physician to ablate tissue during open heart surgeryfor mitral valve replacement.

[0211] Various features of the invention are set forth in the followingclaims.

We claim:
 1. An electrode support structure comprising a guide bodyhaving a distal end, a flexible spline leg having an axis attached tothe distal end of the guide body, the spline leg being flexed to definean arcuate shape, an electrode element carried by the spline leg formovement along its axis, and a control element coupled to the electrodeelement for remotely imparting force to move the electrode element alongthe axis of the spline leg.
 2. An electrode support structure comprisingfirst and second flexible spline legs, each having a near end and a farend, the near ends positioned in a circumferentially spaced relationshipwith the far ends joined at a junction to define an arcuate shapebetween the near ends of the first and second spline legs, an electrodeelement carried by at least one of the spline leg for movement along it,and a control element coupled to the electrode element for remotelyimparting force to move the electrode element along the at least onespline leg.
 3. An electrode support structure comprising a guide bodyhaving a distal end, a stiffener extending along an axis outside thedistal end of the guide body, at least one flexible spline leg having anear end attached to the distal end of the guide body and a far endextending beyond the distal end of the guide body and attached to thestiffener, the spline leg being normally flexed between the distal guidebody end and the stiffener in an arcuate shape that extends along andradially outward of the axis of the stiffener, an electrode elementcarried by the at least one spline leg for movement along it, and acontrol element coupled to the electrode element for remotely impartingforce to move the electrode element along the at least one spline leg.4. A support structure according to claim 3 wherein the control elementcomprises at least one control wire that travels along the stiffener tothe electrode element on the at least one spline leg.
 5. A supportstructure according to claim 1 or 2 or 3 wherein the guide body includesa proximal end, and wherein the control element is located at theproximal end of the guide body.
 6. A support structure according toclaim 1 or 2 or 3 wherein the control element includes a first controlwire to impart force to move the electrode element in a direction towardthe near end of the at least one spline leg and a second control wire toimpart force to move the electrode element in a direction toward the farend of the at least one spline leg.
 7. A support structure according toclaim 1 or 2 or 3 wherein the electrode element comprises at least twobi-polar electrodes separated by an electrically insulating material. 8.A support structure according to claim 1 or 2 or 3 wherein the electrodeelement comprises at least one unipolar electrode mounted on a core bodyof electrically insulating material.
 9. A support structure according toclaim 8 wherein the electrode comprises a coil wound about the corebody.
 10. A device for ablating tissue comprising a guide body having adistal end and a proximal end, a flexible spline leg having an axisattached to the distal end of the guide body, the spline leg beingflexed to define an arcuate shape, an ablation electrode element carriedby the spline leg for movement along its axis, and a control element onthe proximal end of the guide body and being coupled to the ablationelectrode element for remotely imparting force to move the ablationelectrode element along the axis of the spline leg.
 11. A supportstructure according to claim 10 wherein the ablation electrode elementcomprises at least two bi-polar electrodes separated by an electricallyinsulating material.
 12. A support structure according to claim 10wherein the ablation electrode element comprises at least one unipolarelectrode mounted on a core body of electrically insulating material.13. A support structure according to claim 12 wherein the electrodecomprises a coil wound about the core body.
 14. A support structureaccording to claim 10 wherein the control element includes a firstcontrol wire to impart force to move the ablation electrode element in adirection toward the near end of the at least one spline leg and asecond control wire to impart force to move the ablation electrodeelement in a direction toward the far end of the at least one splineleg.
 15. A method for ablation tissue in a heart comprising the steps ofintroducing a probe into the heart, the probe carrying at least oneelongated spline leg flexed outward of the probe to define an arcuateshape, the probe also including at least one ablation electrode that ismovable along the at least one spline leg spline in response to theapplication of force, establishing contact between the ablationelectrode and a region of heart tissue, the spline leg defining anelongated path along the tissue region, transmitting ablation energy tothe ablation electrode while in contact with the tissue region, andapplying force to move the ablation electrode along the at least onespline leg while maintaining contact with the tissue to ablate tissuealong the elongated path.
 16. A method for ablation tissue in a heartcomprising the steps of introducing a probe into the heart, the probecarrying at least one elongated spline leg flexed outward of the probeto define an arcuate shape, the probe also including at least oneablation electrode that is movable along the at least one spline legspline in response to the application of force, establishing contactbetween the ablation electrode and a region of heart tissue, the splineleg defining an elongated path along the tissue region, and applyingforce to move the ablation electrode along the at least one spline legwhile transmitting ablation energy to the ablation electrode to ablatetissue along the elongated path.